1. Field of the Invention
The present invention relates to a transmission system, and more particularly to an apparatus and method for measuring the bit error ratio of a transmission system.
2. Background of the Related Art
Typically, in a transmission system, such as a fiber loop carrier (FLC) for example, service quality of a corresponding line is measured by calculating the bit error of all signals received by means of E1, DS1, DS3, STM-1, etc. In addition, the degradation of service quality must be determined according to a method for measuring the Bit Error Ratio (BER), and the result must be reported to the operator of the transmission system by means of warning or event reporting.
In a related art BER measuring method, where the BER for determining that the service quality of a transmission line in a normal state is unacceptable is set to 10E-3, and the BER for determining that the service quality of a transmission line in an abnormal state is acceptable is set to 10E-4, a counter is incremented according to the number of errors generated, and a line failure alarm is generated if errors continue at the ratio of 10E-3 for an alarm occurrence duration time (e.g., 2 seconds) for deciding a line failure generation. In addition, after the error generation, if there is no error for an alarm clearing duration time (e.g., 10 seconds) for deciding the repair of the line failure, or if errors continue at the ratio of less than 10E-4, the release of the line failure is determined.
In the above-described related art method for measuring the BER, if the generation of an bit error of a transmission line continues for a predetermined time (alarm generation duration time) at more than a certain ratio, a line failure alarm can be generated.
However, where excessive error is generated instantaneously (for example, when excessive error exceeding 10E-2 within one second is generated in a 2-second interval), an alarm may be not generated even though an error exceeding 10E-3 BER is generated. In addition, when an error is generated intermittently after an error generation (e.g., when an error exceeding 10E-4 for one second of 10 seconds is generated), the alarm may be not cleared and the alarm state may be continued even though the error generation ratio has decreased to less than 10E-4.
As illustrated in FIG. 1, when excessive error is generated instantaneously, with the number of errors being 2*N3 at a period of time T, 0 at a period of time 2T, and 2*N3 at a period of time 3T, the BER at this time is termed Excessive-BER (E-BER). Here, N3 is the number of error generation of 10E-3 BER during a predetermined period of time T, and AG is a bit error counter.
In addition, a bit error counter, E-BER generation flag, and E-BER clearing flag are placed at each line of the transmission system. Then, a bit error value is read and is accumulated at a time interval of t (e.g., 10 ms) which is less than the period of time T.
Accordingly, when time T begins, the system determines whether or not the count value of the bit error counter exceeds the BER of time T. If it does, the E-BER generation flag is set. If the bit error count value exceeds the BER of time T at the next period of time T, it is determined that the E-BER is continuously maintained. However, if the bit error counting value becomes less than the BER of time T at the next time T, the E-BER generation flag is reset and the BER calculation is started again at the next period of time T.
Consequently, if the E-BER generation flag is set and continued during an alarm generation duration time, an E-BER alarm is generated. In addition, after the generation of the E-BER alarm, if the bit error count value is calculated at an interval of time T, and is continuously maintained at less than an alarm clearing BER, the E-BER alarm is cleared.
In the related art method for measuring the bit error ratio of a transmission system, when excessive error is continuously or instantaneously generated as illustrated in FIG. 1, there is a problem that an E-BER alarm is erroneously not generated because an error is not generated during an alarm generation duration time.
In addition, after the generation of an alarm, when an error is maintained intermittently for a long period, there is a problem that an E-BER alarm is not cleared although an E-BER alarm must be cleared because an error is generated at less than an alarm clearing BER.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.